Despite significant advances in the techniques used for its control during recent decades, the mosquito continues to pose serious public health problems as we approach the 21.sup.st Century. In addition to the persistent irritation they cause humans and animals simply by virtue of their blood-sucking behavior and the itching this causes, mosquitoes are also the principal vector of a variety of serious diseases, including malaria, yellow fever, dengue, and encephalitis. Worldwide, approximately 2.7 million human deaths occur each year solely as a result of malaria transmitted by mosquitoes [1].
We disclose herein the use of alkanols applied to water as soluble solutions for the control of mosquitoes in their larval stage. Exemplified species include Culex tarsalis, the principal vector of the Western equine and St. Louis encephalitis viruses common throughout the Western U.S., and Culiseta incidens. To understand the molecular basis of alkanol toxicity, a variety of unsaturated long-chain alcohols were also tested, including, farnesol which may act in some insects as a juvenile hormone mimic [2].
Primary alkanols are important flavor and fragrance compounds that are found throughout the plant kingdom, occur naturally in everyday foods and beverages [3], and are widely used as food additives [4]. Homologues containing 12 or more carbons are only sparingly soluble in water and their tendency to form monomolecular layers over the surface of a body of water was examined decades ago as a means to reduce evaporative losses [5]. Because monolayers lower surface tension, it was also suggested that they might be used in pest control to suffocate the aquatic stages of mosquitoes or prevent recently emerged adults from launching off the water's surface. Consequently, all earlier research employing alkanols against mosquitoes has attributed lethality entirely to reduced surface tension, wetting of their hydrofuge structures, or other surface-related phenomena [6-10]. However, here we disclose that there is a more immediate and lethal effect of 1-alkanols on mosquito larvae, that it is unrelated to surface tension, and is biochemical rather than physical.
A review of the literature indicates that this is the first comprehensive study of the structure-activity relationship for the full series of alkanols against mosquitoes. Primary alkanols are also known to act as general anesthetics [11,12], and increasing potency has been correlated to increasing chain length [13] until a point of cutoff is reached, usually at 1-dodecanol, after which activity disappears entirely [14,15]. In mosquitoes, we found that activity levels off after undecanol (C.sub.11) but does not disappear until after pentadecanol (C.sub.15). Mosquitoes appear to be the first animal for which cutoff has been demonstrated to occur at a chain length beyond C.sub.12, offering new insights into the molecular basis of anesthetic cutoff and demonstrating that alkanols may be used for selective pest control.
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